Genetic and functional identification of the likely causative variant for cholesterol gallstone disease at the ABCG5/8 lithogenic locus

Abstract

The sterolin locus ( ABCG5/ABCG8 ) confers susceptibility for cholesterol gallstone disease in humans. Both the responsible variant and the molecular mechanism causing an increased incidence of gallstones in these patients have as yet not been identified. Genetic mapping utilized patient samples from Germany (2,808 cases, 2,089 controls), Chile (680 cases, 442 controls), Denmark (366 cases, 766 controls), India (247 cases, 224 controls), and China (280 cases, 244 controls). Analysis of allelic imbalance in complementary DNA (cDNA) samples from human liver (n = 22) was performed using pyrosequencing. Transiently transfected HEK293 cells were used for [3H]-cholesterol export assays, analysis of protein expression, and localization of allelic constructs. Through fine mapping in German and Chilean samples, an ˜250 kB disease-associated interval could be defined for this locus. Lack of allelic imbalance or allelic splicing of the ABCG5 and ABCG8 transcripts in human liver limited the search to coding single nucleotide polymorphisms. Subsequent mutation detection and genotyping yielded two disease-associated variants: ABCG5-R50C ( P = 4.94 × 10−9) and ABCG8-D19H ( P = 1.74 × 10−10) in high pairwise linkage disequilibrium ( r 2 = 0.95). [3H]-cholesterol export assays of allelic constructs harboring these genetic candidate variants demonstrated increased transport activity (3.2-fold, P = 0.003) only for the ABCG8-19H variant, which was also superior in nested logistic regression models in German ( P = 0.018), Chilean ( P = 0.030), and Chinese ( P = 0.040) patient samples. Conclusion : This variant thus provides a molecular basis for biliary cholesterol hypersecretion as the mechanism for cholesterol gallstone formation, thereby drawing a link between “postgenomic” and “pregenomic” pathophysiological knowledge about this common complex disorder.

The Neglected Cousin of the Hepatocyte: How Gallbladder Epithelial Cells Might Contribute to Cholesterol Gallstone Formation

“…Interestingly, the ABCG5/G8 locus has also long been implicated in the formation of cholesterol gallstones [10]. Recently, specific coding variants have been identified in genome-wide association studies that likely result in a gain-of-function of ABCG5/G8, supposedly translating into increased biliary cholesterol secretion [11]. Neither in animal experiments nor in human material has the functionality of ABCG5/G8, specifically in the gallbladder, been explored; although, derived from their function in liver and intestine increasing cholesterol secretion into bile would be expected.…”

Cholecystectomies at Rims, Ongole- A Retrospective Analysis

“…2 Genetic and functional identification of the likely causative variant for cholesterol gallstone disease is at the ABCG5/8 lithogenic locus. 3 The prevalence of gallbladder stones is higher among patients with chronic kidney disease in Taiwan. 4 Susruta described jaundice called pittaash mari janya meaning a jaundice caused by stone in bile.…”

Modifiable Factors and Genetic Predisposition Associated with Gallbladder Cancer. A Concise Review

“…Candidate genes tested in human cohorts include for example the apolipoproteins E (APOE) [58] and B (APOB) [59,60], cholesterol 7 α-hydroxylase [61,62], cholecystokinin receptor A (CCKAR) [63], the low density lipoprotein receptor related protein-associated protein (LRPAP1) [64] and the cholesterol ester transporting protein (CETP) [65]. Finally, genome-wide association analyses and functional studies have identified the p. D19H variant of the hepatic cholesterol hemitransporter (ABCG8) associated with susceptibility for human gallstones [55,66,67]. To our knowledge the only genome-wide association study (GWAS) of patients with gallbladder cancer published to date (https://www.ebi.ac.uk/gwas/) was conducted in a relatively small Japanese discovery cohort of 41 GC patients and 866 controls, and a subsequent validation cohort of 30 cases and 898 controls [68].…”